17.4: The Role of Dopant Materials on Current Efficiency Roll‐off in Organic Light‐Emitting Diodes

Self Cite

In mass production OLED structures, doping ratio distribution across the thickness of emitting layer is not uniform owing to the linear evaporating configuration, where dopant and host materials are added in different sources. In this study, we firstly confirmed that different types of doping distribution among emitting layer of green phosphorescent OLED exhibited over 15% difference of current efficiency. By carefully designing and comparing emitting layers with a series of doping distribution modes, we found that dramatic variation of doping ratio near electron blocking layer was the critical factor. Then, trapping behavior of dopant molecules was confirmed to affect the carrier distribution among the emitting layer according to analysis of current density‐voltage (JV) and capacitance‐voltage (CV) curves from carrier only devices based on two types of doping distribution modes. Combining with the result of hole‐electron recombination zone (RZ), the area where possessed both high doping ratio and excitons recombination probability exhibited a high current efficiency and low driving voltage. Finally, PL and EL transient decay lifetime combined with triplet‐polaron quenching (TPQ) efficiency measurement demonstrated that TPQ was the main factor causing current efficiency difference between two types of doping distribution modes. Therefore, the doping distribution and trapping property of dopant material in emission layer should be carefully evaluated for OLED devices for mass production.

Section: Carrier Behaviors Of the Devices Based On Two Doping Distrib...mentioning

confidence: 99%

Section: The Tpq and Excited State Behavior Of Two Doping Distributio...mentioning

confidence: 99%

11.2: The Effect of Doping Distribution on the Property of Green Phosphorescent Organic Light‐Emitting Diodes

Liu¹,

Li²,

Yao³

et al. 2023

Self Cite

“…While novel emitters and tuning host systems have the potential to reduce capacitance, striking a balance to maintain essential device performance metrics simultaneously, such as efficiency and lifetime, proves to be challenging. Conversely, studies indicate that the careful selection of transport materials and optimization of device stacks can significantly influence the CV characteristics of OLEDs [3][4][5][6]. Thus, achieving lower capacitance through device structure optimization without changing EML composition is feasible while preserving essential performance parameters.…”

Section: Introductionmentioning

confidence: 99%

70‐1: Invited Paper: Capacitance Reduction of Red OLED through Device Optimization

Xie,

Pang,

Cui

et al. 2024

In this work, we demonstrate a novel device structure with a dual‐electron blocking layer (2EBL) configuration to improve the capacitance‐voltage (CV) behavior without compromising other critical performances of bottom‐emission red organic light‐emitting diode (OLED). We started the work from studying the influence of electron blocking materials (EBMs) on various device characteristics including capacitance behavior. It is found that with conventional single EBL configuration, EBM with a deep highest occupied molecular orbital (HOMO) level tends to have high voltage yet low capacitance, while EBM with a shallow HOMO has the opposite behavior. To combine the advantages of low voltage and low capacitance, we investigate the employment of 2EBL configuration. 2 EBMs were developed, where EBM1 has a HOMO of ‐5.17 eV and a faster hole mobility of 21×10‐5 cm2/Vs, while EBM2 has a deeper HOMO level of ‐5.22 eV and a slower mobility of 14×10‐5 cm2 /Vs. Bottom emission red OLEDs A‐D with single EBM1, single EBM2, EBM1/EBM2, and EBM2/EBM1 were fabricated, respectively. The characterization of OLEDs A‐D reveals that OLED C reaches a balanced performance, at 10 mA/cm2 achieving a low voltage of 3.5 V, a low maximum capacitance per unit area (u‐Cmax) of 36 nF/cm2 and an accumulated charges per unit area (u‐Q) of 8 nC/cm2, while maintaining a high EQE of 30.6% and a long lifetime LT95 of 11,300 h. Moreover, Electrochemical Impedance Spectroscopy (EIS) measurements highlight the differences in bulk resistance among the OLED configurations, emphasizing the importance of EBL composition and arrangement in optimizing OLED performance. Low capacitance of OLED ensures a quick signal response and hence quick refresh rate, especially at low gray scale scenarios. Reduction of capacitance through EBL optimization is believed to be the best strategy, comparing to tuning emitter and hosts which is more likely to affect other key performances of OLED. Although this work is based on study of red OLED, the same scheme can be extended to other colors.

“…This causes a cumulative effect, resulting in subsequent processing of the film layer of process stability difficulties to enhance. Therefore, tapping a more accurate surface analysis method for multi-film layer analysis is currently a limitation of OLED process inspection difficulties (3)(4)(5).…”

Section: Introductionmentioning

confidence: 99%

29‐4: TOF SIMS for OLED Film 3D Detection and Real‐Time Failure Analysis

Zheng,

Fu,

Shi

et al. 2024